With the rapid development of information system in society, a photoelectronic component and equipment have been markedly advanced and popularized. Among other things, a display has spread wide for use in a television set, a personal computer, or the like, and the display is required for increasing a size thereof as well as decreasing thickness thereof. A plasma display has attracted attention as a thin-type display in a large size. However, on the basis of a structure and an operational principle thereof, the plasma display emits an intense leakage electromagnetic field and a near-infrared ray from a display screen.
In recent years, an influence of the leakage electromagnetic wave on the human body and other electronic equipment has come to be a topic to be discussed, and, for example, it has become necessary to keep the leakage electromagnetic wave within limits set by VCCI (Voluntary Control Council for Interference by Data Processing Equipment and Electronic Office Machines) in Japan.
Moreover, there is a possibility that the near-infrared ray emitted from the display screen may act on the electronic equipment such as a cordless phone located around the display and cause malfunction thereof. Since near-infrared rays having wavelengths of 820 nm, 880 nm, 980 nm and the like are used in a remote controller and optical communication by a transmission system, it is necessary to suppress light having a wavelength in a range of from 800 to 1100 nm which is in a near-infrared region to such a level as does not cause a problem in practical use.
With regard to cutting-off of the near-infrared ray, it has been known that a near-infrared absorption filter produced by using a near-infrared absorbing dye is used. However, since the near-infrared absorbing dye is liable to be deteriorated by environmental factors such as humidity, heat and light, there is a tendency that the near-infrared absorption filter which uses the dye may undergo changes in optical properties such as decrease in near-infrared ray cutting-off capacity, and a change of a color transmitted through the filter with the lapse of time.
Since the plasma display emits the intense near-infrared ray over a wide wavelength range, it is necessary to use the near-infrared absorption filter having a high absorption index for the near-infrared region over a wide wavelength range. However, in a conventional near-infrared absorption filter, only a near-infrared absorption filter in which visible light ray transmittance is low has been realized.
In order to cut off the leakage electromagnetic wave, it is necessary to cover a surface of the display screen with an electrically conductive substance having high electric conductivity. A transparent electrically conductive layer is ordinarily used as such a method and, on this occasion, such transparent electrically conductive layers are broadly classified into 2 categories: an electrically conductive mesh; and a transparent electrically conductive thin film. As the electrically conductive mesh, ordinarily used is a grounded metallic mesh, a synthetic fiber mesh or a metallic fiber mesh which has been coated with a metal, an etched film which has been produced by first forming a metallic film and then performing an etching treatment on the thus-formed film in a lattice pattern manner or the like.
There is a method to use a transparent electrically conductive thin film comprising a metallic thin film, an oxide semiconductor thin film and the like as an electromagnetic wave shielding layer, instead of using the electric conductive mesh. However, the metallic thin film can obtain favorable electric conductivity, but fails to provide a high visible light ray transmittance owing to reflection and absorption by the metal over a wide wavelength range. The oxide semiconductor thin film has higher transparency than that of the metallic thin film, but is inferior in electric conductivity and near-infrared reflectivity. As described above, with reference to the transparent electrically conductive layer for the purpose of cutting-off the leakage electromagnetic field, there are many cases in which, when the shield capacity thereof is regarded as being important, the electrically conductive mesh is used while, when cost performance is regarded as being important, the transparent electrically conductive thin film is used.
Further, a method using a dye for trying to improve a color purity of the display is described in, for example, Japanese Unexamined Patent Publication JP-A 58-153904 (1983), JP-A 60-22102 (1985), or JP-A 59-221943 (1984) and the like. An application thereof to a plasma display panel is recited in JP-A 58-153904.
However, in these prior arts, there is no recitation on a combination of a transparent electrically conductive layer as electromagnetic wave shielding which is essential when applied to the plasma display panel and a dye, and there is also no specific recitation on the dye to be used.
It is considered that a plasma display filter is formed separately from the display and, then, disposed as a front surface panel of the display for the purposes of cutting off the near-infrared rays and electromagnetic waves, and protecting the display screen. However, such a front surface panel method brings about a cost increase owing to a many number of components and/or production processes of the plasma display filter whereupon it becomes difficult to allow the plasma display filter to be smaller in thickness and lighter in weight.
Further, reflection on a surface of a representation portion of the plasma display is not ordinarily decreased and reflectance of a glass substrate is maintained; on this occasion, when the front surface panel is disposed apart from the representation portion from a viewpoint of thermal design and the like, a reflected image becomes double-or-more-images caused by reflections of external light on the display surface and the front surface panel whereupon there is a case in which visibility of the display is deteriorated. Still further, the plasma display has characteristics that, due to reflection of glass or phosphor on the surface of the screen, contrast in a bright place is low as well as a color reproduction gamut of luminescence is narrow.
On the other hand, methods of removing the front surface panel and, then, directly bonding an optical film on the display panel are proposed in Japanese Unexamined Patent Publications JP-A 10-156991 (1998), JP-A 10-188822 (1998), JP-A 2000-98131 (2000) and the like. However, any of these prior arts does not define total thickness of a whole transparent polymer film and does not specifically recite provision of shock resistance.
To contrast, in Japanese Unexamined Patent Publication JP-A 10-211688 (1998), it is proposed that, in order to absorb shock from outside, an optical film for use in direct bonding is laminated on a transparent polymer sheet having a thickness of 1 mm or more and the resultant laminate is used. However, it is difficult from a practical point of view that the transparent polymer sheet having a thickness of 1 mm or more in roll form is subjected to a continuous bonding process or is directly bonded on the display and, as seen in an embodiment, since bonding is performed to an acrylic sheet having a thickness of 3 mm, it is apparent that an improvement of a known front surface panel type filter based on sheet bonding has been intended.
Ordinarily, the transparent polymer film having various types of functions in application fields according to the present invention is used in roll form and, from the standpoint of operational efficiency and the like, the transparent polymer film having a thickness of from 75 to 100 μm is used. Therefore, when 2 sheets of the transparent polymer films each having a function are simply bonded with each other, a total thickness merely comes to be less than 0.3 mm. Further, as an anti-reflection film, that having a thickness of 188 μm has been used in some cases and, in these cases, a base film thereof was polyethylene terephthalate (PET); however, since it is inferior in an anti-reflection property to triacetyl cellulose (TAC) in which a favorably used base film is 80 μm thick, it is not used in a positive manner for the purpose of bonding films with each other.
Further, when a film is directly bonded on a display panel body, since the display itself is expensive, it is indispensable to remove the film for a treatment at the time a problem occurs; however, in the foregoing patent, there is no recitation on workability of this type. Still further, though bonding of the film to the display has already been performed in a liquid crystal display, a flat television set and the like, since the plasma display comes to be substantially large in size, there are operational problems that it is troublesome to require much force in removing the film therefrom than that in a conventional display, a paste tends to remain on the surface of the display and the like.
Further, in an electromagnetic wave shielding body, it is necessary to establish conduction between the transparent electrically conductive layer and an outside by using an electrode which leads the electromagnetic wave out to the outside as an electric current. As a method to attain such a necessity, there is mentioned that, when a film is bonded on the transparent electrically conductive layer for a protection purpose and the like, the film is bonded such that a portion of the layer is exposed on a periphery of the filter to allow the thus-exposed portion to become a position which performs electric conduction with the outside as an electrode. Conventionally, the electromagnetic wave shielding body obtained by bonding the film to the front surface panel has established conduction with the outside by this method. As methods of exposing the transparent electrically conductive layer, various types of methods have been performed, for example, a method in which a surface area of the film to be bonded on the transparent electrically conductive layer is allowed to be a little smaller than that of the transparent electrically conductive layer and other methods.
When this method is applied, since it is necessary to perform a two-step bonding operation in which a film comprising a transparent electrically conductive layer is first bonded in a sheet state to a plate having high rigidity or the like and, then, a protective film having a little smaller area than that of the resultant bonded material is further bonded in a sheet state to the resultant bonded material, there is a problem in productivity.
Further, in the electromagnetic wave shielding body conventionally obtained by bonding the film to the front surface panel, an electrode has been disposed on an entire peripheral portion thereof. When such a method is used, since it is necessary to perform an electrode forming operation in a sheet state, there is a problem in productivity.
In view of the conventional methods, it is an object of the invention to provide a display filter which has desired filter characteristics such as electromagnetic wave shielding capacity, near-infrared ray cutting-off capacity, and image improvement capacity and which is capable of aiming for improvements such as a low cost, a lighter weight, a smaller thickness, a panel protection, workability when a trouble occurs, and enhancement of productivity, a display apparatus mounted with the filter, and a method for production of the same.